Electrical power generation from primary energy sources is becoming one of the most concerned issues in the world. Traditional energy conversion techniques relies mainly on fossil fuels combustion. The combustion of fossil fuels has been identified as the major source of global warming and air pollution. The climate change in recent years requests urgent development of high efficiency clean energy systems. Fuel cell system is one of the alternative energy conversion systems that potentially has a high energy conversion efficiency. Various types of fuel cells have been developed in recent decades. Among them, solid oxide fuel cells (SOFCs), which normally operate in the high temperature range from about 600° C. to about 1000° C., could be combined with other thermal cycles to improve the thermal efficiency and to have high tolerance for sulfur components and carbon monoxide (CO). Coincidentally. CO is also a fuel for SOFCs. Therefore, SOFCs could be fuelled up by synthesis gas obtained from reforming of infrastructure fuel, such as diesel fuel, using as an auxiliary power unit (APU) in automotive applications, for instance.
Diesel fuel reforming can be carried out by three different mechanisms: steam reforming (SR), partial oxidation (POX) and auto-thermal reforming (ATR). Catalytic ATR, which may be viewed as a combination process of SR and POX, besides its well-known high energy efficiency, has shown unique advantages in scavenging carbon deposited on catalyst by super-heated steam and producing high selectivity of hydrogen.
The study of catalytic ATR of diesel fuel started in early 1980s using traditional Ni-based catalyst. Recent progresses in liquid hydrocarbon reforming catalytic systems have found that noble metals such as Rh, Pt and Pd supported on refractory oxide exhibit superior catalytic reactivity over the traditional Ni-based catalyst in terms of preventing carbon deposition and sulfur poisoning. Studies have also shown that certain Rh-based catalysts perform exceptionally well. However, as Rh is among the most expensive precious metals available, it is economically unfeasible to rely on Rh-based catalysts for devising an APU to power fuel cells on a long term basis. While Ni-based catalysts are much more abundant and are therefore cheaper than noble metal-based catalysts, Ni-based catalysts nevertheless face the problem of carbon deposition during the diesel fuel reforming.
Traditionally, alumina-based materials were used as a catalyst support for the Ni-based catalysts. In recent years, catalyst supports formed of oxygen anion conducting materials, such as doped ceria, zirconia and their mixed composites, have been shown to afford higher resistance to carbon deposition and sulfur poisoning compared to alumina-based supports. For example, ceria-based oxygen anion conducting material has been used as a support for Ni nanoparticles. Ni nanoparticles supported on ceria-based supports have been found to show resistance to carbon deposition during methane reforming, but not during dodecane or hexadecane reforming.
Supported catalysts are traditionally made by impregnation method. In the case of Ni nanoparticles supported on ceria made by impregnation method, most of the Ni nanoparticles surfaces do not contact with the ceria, and thus are not protected by ceria against sintering and thereafter carbon deposition and sulfur poisoning. As a result, conventional supported Ni-based catalysts are vulnerable to deactivation due to carbon deposition and adsorption of sulfur-containing compounds that are present during the reaction of reforming diesel oils.